I have some hairy questions: What is the
difference between fur and hair? Why is my
hair growing and growing but my dogs hair does
not? Why did humans loose most of their body
hair while apes did not? Why did evolution
make hairy creatures?

Question Date: 2002-09-24

Answer 1:

Let's see if we can get to the root of some of you
hair questions (sorry about that). I'm a
mammalogist (someone who studies mammals)
so hair
questions are interesting to me. All mammals have
hair at some point in their lives (whales have
hair before they're born). What other
characteristic do all mammals have?Fur and
hair are the same thing, we just use different
words for it. There are different types of hair.
The hair that makes up your eyelashes is
different from the hair on your head or the very
fine hair on the back of your hand. If you look
at a cat or dog, you'll see that they have
different types of hair too. They usually have a
thick, wooly under-coat covered by longer, thicker
hairs. They have "whiskers" on their face that
help them sense movement in the dark.

So
why is your dog's coat a certain length?
Take a
look at the hair on your arm. You will notice
that it only gets to a certain length and stops.
All hair grows for a certain amount of time, then
stops. The hair on a human head just grows for a
longer time than dog hair or human arm hair.
Human scalp hair grows about 0.35 mm per day. The
hair follicle stays active, producing the hair,
for about 500-800 days. How long can the hair on
your head grow? How fast any one person's hair
grows, and how long it keeps growing is
determined
by that person's genes.

Why did humans
lose most of their body hair while apes did not?
We actually still have hair everywhere except for
the palms of our hands, the soles of our feet, and
our lips. You and I have about as many hair
follicles as a chimp has, but each of our hairs
(except for the ones on our heads) is a lot
shorter. Why is our hair so much shorter? I
usually think about these questions by thinking
about what's good and bad about something (costs
and benefits). We think humans evolved in hot,
sunny places. Hair would help to protect us from
the sun, but would be more likely to give
parasites (ticks, fleas, and lice, for example) a
place to hide. Losing most of our hair would
reduce the parasites we carried around. We could
have protected ourselves from the sun in other
ways, such as wearing clothing. Head hair would
keep the sun off of us where we'd get the most
sun. No one really knows, though. What do you
think?

Why did hairy animals evolve?
Mammals and birds are different from most animals
because we create body heat rather than depending
on heat from outside our bodies. The word for
this is "endothermic," but a lot of people
call it
being "warm blooded". Making all this heat
takes
a LOT of energy, so we need insulation to keep it
in. Fat is a good insulator. So are hair and
feathers.Why do you think marine mammals like
whales and dolphins use fat instead of hair for
insulation?

Answer 2:

I assume that you are referring to the hair on
your head. While it is indeed true that the hair
on your head grows the longest of any of that on
the remainder of your body, virtually all body
hair is genetically predetermined to grow a
certain length. You can easily test this by
shaving off your eyebrows and watching them
re-grow to their current length (I do not,
however, recommend this as eyebrow-less people
look a little strange. Just look at Mona Lisa.
Perhaps she too was interested in this question
yet failed to realize the time required for her
eyebrow hair to re-grow before scheduling her
portrait painting session). You could also shave
off a small patch of arm hair and observe a
similar effect. Also, if you were to shave your
dog, its hair would grow back to approximately its
original length.

Why did humans loose most of
their body hair while apes did not? While there
is not a clear-cut answer to this question, there
was obviously some evolutionary pressure that
selected against extensive hairiness in early
humans. Since it is suggested that early man may
have evolved in tropical Africa, one can imagine
that excessive hairiness might have been a major
disadvantage as man began to colonize dryer and
hotter climates. With a gradual evolutionary loss
of large quantities of body hair, there was also a
subsequent increase in solar exposure and an
increased susceptibility to skin cancer. To
counteract this, natural selection favored
survival of humans with increased skin melanin
concentration, which acted as a natural sunscreen,
protecting these early people. As humans began to
colonize the rest of the world and subsequently
invade colder climates, there was less of a demand
for large concentrations of dermal melanin and
subsequently, over evolutionary time, these people
reverted to a lighter skin color. This is,
however, only one possible explanation and several
alternative hypotheses have been put forth to
explain this. Most apes probably lacked the
intellectual capacity to survive in unfamiliar
habitats and thus, there was only a demand to
retain the necessary quantity of hair to survive
in the climate to which they were
pre-adapted.

Why did evolution make hairy
creatures? Hair serves several important
functions, but one of its most important is that
of an insulator. Furry creatures are better
adapted for invading colder climates or nocturnal
habitats (remember that furriness often goes along
with warm-bloodedness). Those species with the
most hair (or that functioned as the best
insulator) were able to survive colder
temperatures and eventually out-compete their
hair-challenged counterparts, assuring survival of
the species and the appearance of hairy
individuals in future generations.

Answer 3:

Wow, you asking the tough "why" questions here!
Let's start with number 1: is there really a
difference between fur and hair? At a basic level,
"no." All mammals have hair (well, except for
adult cetaceans -- whales and dolphins -- who
actually lose their baby hair and replace it with
layers of insulating blubber ). The "hair" has
varying degrees of thickness, color, texture, and
structure. And depending on these characteristics,
we call it "fur" v "hair." Your dog's hair does
grow -- but it falls out and is replaced before it
gets too long. Did you see the movie "Lord of the
Rings" or read the book or the prequel, "The
Hobbit"? (By the way, I liked the movie, but the
books are even better!) If so, you read/saw that
hobbits have "furry" feet. Their feet have "hair"
on them but because of how that hair looks, the
word "furry" is used. It just gives you a
different idea of what the hair is like.

Now we
get to these "why" questions. It is really, really
difficult to be certain about "why" something
might have come about. But let's think it through
--the "simplest" explanation is what we want to
start with as a scientist. Neither dogs nor
humans have always lived in warm, protected
houses, right?Dogs rely on their fur
coats for
warmth and protection from the elements and dogs
have been bred to "select for" certain types of
coats (compare and English sheep dog with a
chocolate lab). Apes rely on their fur for
protection and warmth, too. Most loss of body heat
in a human is through the head (where our big
brains are being supplied lots of warm blood close
to the surface). We still have hair on our
heads... Do you see where this is going? We cannot
ever "prove" that humans lost most of their body
hair because they no longer needed it to stay warm
and protected, but we can hypothesize about
it.

There are other possibilities as well -- think
them all through and then stick with the simplest
one. If you can disprove that hypothesis, then
move to the next one. It's the way science works!
You always disprove things as opposed to having
absolute proof of something. And keep asking those
tough questions!